1. Field of the Invention
The present invention relates to a dental impression material kneading device for discharging two kinds of pastes of a dental impression material respectively, and mixing and kneading the both pastes in a mixer body. The dental impression material comprises the two kinds of pastes having different fluidities at the time of a feed start, and the mixer body comprises a stirring rod and an outer case mounted around the stirring rod.
2. Description of the Conventional Art
As a general dental impression material comprising the two kinds of pastes, a dental alginate impression material, a dental silicone rubber impression material and the like are commonly known. The dental alginate impression material is made by kneading a substrate paste containing alginic acid salt as a main component and a curing agent paste containing gypsum as a main component. The dental silicone rubber impression material is made by mixing and kneading a substrate paste and a curing agent paste. The substrate paste contains silicone having Si—H group and silicone having a vinyl group as main components. The curing agent paste contains silicone having a vinyl group and a platinum catalyst as main components.
Further, such the conventional dental impression material comprising two kinds of pastes is made by mixing and kneading each paste with a fixed mixing ratio beforehand. However, in recent years, the dental impression material comprising the two kinds of pastes, where a viscosity of the dental impression material in a paste state after mixing and kneading can be arbitrarily adjusted by mixing and kneading the two kinds of pastes at a changed mixing ratio of each paste within the prescribed range was developed. (Hereinafter, “this dental impression material comprising the two kinds of pastes, where a viscosity of the pastes of the dental impression material can be arbitrarily adjusted after mixing and kneading by changing the mixing ratio of each paste within the prescribed range” is said to as “the dental impression material having the arbitrarily adjusted viscosity”.) In the case of mixing and kneading such the dental impression material having the arbitrarily adjusted viscosity, the material may be mixed and kneaded after each paste being discharged so as to have the mixing ratio of the both pastes of, for example, 1:3, 1:6, 1:9 or the like, in order to obtain a dental impression material having the desired viscosity after mixing and kneading.
As a device for mixing and kneading such the dental impression material comprising two kinds of pastes, there has been widely used a dental impression material kneading device comprising two parts, one of which discharges each paste of the dental impression material comprising the two kinds of pastes, and the other of which mixes and kneads the both pastes in a mixer body comprising a stirring rod and an outer case mounted around the stirring rod. More particularly, for example, the device comprising a paste feed means, an outer case, a stirring rod and a rotation means (for example, referring to Japanese Patent Laid Open No. 2000-116675) is used. The paste feed means comprises a first paste flow passage extending to a first paste outlet opened at a front end face, and a second paste flow passage extending to a second paste outlet opened at the front end face. The outer case comprises a cylindrical main part arranged at the downstream side of the front end face of the paste feed means. The stirring rod is rotatably provided in the outer case, having a central axis at a center of the outer case. The rotation means is for stirring by the stirring rod. In this device, when the first paste flowing from the first paste outlet and the second paste flowing from the second paste flow passage pass between the outer case and the stirring rod to flow, these pastes are kneaded by the rotated stirring rod.
However, when such the dental impression material kneading device is used to mix and knead the both pastes of the dental impression material comprising the two kinds of pastes, there are following problems. That is, the two kinds of pastes of the dental impression material have generally different fluidities at the time of feed start since they have different characteristics about moving from a static state respectively. Thus, when each paste is discharged into the outer case of the mixer body in the initial stage of the mixing and kneading, the paste having the low fluidity at the time of feed start is discharged later than the paste having the high fluidity at the time of feed start, so that a time difference is generated. Thus, the dental impression material discharged from an outlet of the outer case of the mixer body in the initial stage is a defective material which is not suitable to make the impression or the like, since the mixing ratio of the both pastes greatly differs from the ratio prescribed beforehand by the time difference at the time of feed start, and thus this material cannot be used and becomes a waste.
Further, when the dental impression material comprising the two kinds of pastes to be mixed and kneaded is the dental impression material having the arbitrarily adjusted viscosity, there are following problems. That is, the time difference generated when the paste having the low fluidity at the time of feed start and the paste having the high fluidity at the time of feed start are discharged into the outer case of the mixer body changes by changing of the mixing ratio of the both pastes even in the case of the same dental impression material. Thus, when the dental impression material having the arbitrarily adjusted viscosity is mixed and kneaded by using such the dental impression material kneading device, the dental impression material discharged from the outlet of the outer case of the mixer body is a defective material which is not suitable to make the impression material or the like, whatever mixing ratio of the discharged pastes may be, since the mixing ratio of the both pastes greatly differs from the desired ratio in the initial stage of the mixing and kneading, and thus such the dental impression material can not be made readily to use.
Then, for solving the time difference generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged into the outer case of the mixer body, and for obtaining the dental impression material comprising the two kinds of pastes in the desired preferable mixing and kneading state in the initial stage of the mixing and kneading, the following mixer body, in which the outer case thereof to be mounted in a dental impression material kneading device is improved, (for example, refer to Japanese Patent Laid Open No. 2000-117080) was proposed, that is, the mixer body comprising a container having a horizontal axis, openings for taking-in each component at a rear end and an injection opening at a front thereof, and a mixing chamber formed in the container, wherein a delay chamber is provided between one of the taking-in openings in the container and the mixing chamber, and extends around the horizontal axis in an arc-shape so as to elongate a passage for flowing one component taken in from one of the taking-in openings.
In this mixer body, the time difference generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged into the outer case of the mixer body can be solved, whereby the dental impression material comprising the two kinds of pastes in the desired preferable mixing and kneading state can be obtained in the initial stage of the mixing and kneading. However, there are following problems. That is, since the delay chamber, which extends around the horizontal axis in the arc-shape so as to elongate the passage for flowing one component taken in from one of the taking-in openings, exists, the paste remained in the mixer body cannot be removed after using, and thus this mixer body cannot be reused. Thus, an unused mixer body must be prepared whenever mixing and kneading, and it is uneconomical. Further, since the used mixer body is thrown away, there is much futility and the time for disposing the waste increases. Furthermore, even if the mixer body has the structure where the delay chamber can be detached, there are following problems. That is, since the delay chamber itself has the complicated structure, a cleaning work for removing the pastes remained in the mixer body, the delay chamber or the like after using, takes time and labor, and thus the time and a labor are spent uselessly. Further, if a time and a labor for carrying out the cleaning work are considered, it may be more economical that the used mixer body is disposed without the cleaning work for removing the remained pastes.
Furthermore, in the case of changing the mixing ratio of each paste of the dental impression material having the arbitrarily adjusted viscosity, there are following problems. That is, the time difference, which is generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged, changes with the mixing ratio of the both pastes. Thus, in order to obtain the dental impression material comprising the two kinds of pastes where the material has the desired mixing ratio and is in the preferable mixing and kneading state in the initial stage of the mixing and kneading, two or more outer cases corresponding to each mixing ratio of the both pastes must be prepared, where each of these outer cases have the delay chamber having the length corresponding to the time difference generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged, so that it is uneconomical. Further, since the outer case corresponding to the mixing ratio of the pastes must be selected and replaced whenever the mixing ratio of the both pastes is changed, it takes time and labor so much, and thus it is not practical.
On the other hand, for solving the time difference generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged into the outer case of the mixer body, and for obtaining the dental impression material comprising the two kinds of pastes in the desired preferable mixing and kneading state in the initial stage of the mixing and kneading, the following dental impression material kneading device with improvement in itself (for example, refer to Japanese Patent Laid Open No. 2000-140600) was proposed. That is, the device comprising, for example, a first paste supply source, a second paste supply source, a kneading means, a first feed pump for feeding a first paste in the first paste supply source to the kneading means through a first paste flow passage, a second feed pump for feeding a second paste in the second paste supply source to the kneading means through a second paste flow passage, a first electric motor for driving the first feed pump, a second electric motor for driving the second feed pump, and a control means for controlling an operation of the first electric motor and the second electric motor, wherein the control means makes the required time difference between rotation starts of the first electric motor and the second electric motor, thereby, although the first and second pastes have the different viscosities and feed flow rates each other, these pastes reaches the kneading means almost simultaneously at the time of feed start, at least one of the first electric motor and the second electric motor is a variable speed electric motor, and the control means adjusts the ratio of a rotational rate of the first electric motor and a rotational rate of the second electric motor, to set the ratio of the feed flow rates of the first paste and the second paste as the prescribed value.
This device solves the time difference generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged into the outer case of the mixer body, and the dental impression material comprising the two kinds of pastes in the desired preferable mixing and kneading state can be obtained in the initial stage of the mixing and kneading. However, when the mixing ratio of the each paste of the dental impression material having the adjusted arbitrarily viscosity is changed in such the device, there are following problems. That is, the time difference, which is generated when the pastes respectively having the low and high fluidities at the time of feed start are discharged, changes with the mixing ratio of the both pastes. Thus, whenever the mixing ratio of the both pastes is changed, setting of the required time difference between the rotation starts of the first electric motor and the second electric motor carried out by the control means, and setting of the ratio of the rotational rates of the first electric motor and the second electric motor must be changed, and thus it takes time and labor so much. Further, when an operator does not understand the time difference or sets this time difference erroneously, it is impossible to obtain the dental impression material having the desired mixing ratio in the preferable mixing and kneading state in the initial stage of the mixing and kneading.